In general, when a vehicle engine is driven, air and fuel needs to be properly supplied to a combustion chamber so that a vehicle is driven as needed by a user. Particularly, as fuel efficiency is now an important issue, a method of increasing fuel efficiency while driving a vehicle with adequate performance is required.
In order to satisfy such requirements, a variable intake system is conventionally mounted in an engine. In such a variable intake system, inlet resistance varies according to revolution bands of an engine and thus directly influences performance of the engine.
As exemplarily shown in FIG. 1, a conventional variable intake system includes an intake manifold including long runners 50, short runners 30 and outlets 70, and valves opened and closed by actuators 90 in the intake manifold.
The operating process of the conventional variable intake system will be described. Air at the outside of a vehicle is introduced into a surge tank 10, the variable intake valve is closed by the actuator 90 (in a state 53), sucked air moves a relatively long distance 50 and, thus, air in the surge tank 10 is provided to a combustion chamber (not shown) through the outlet 70, if the speed of the vehicle is less than a designated speed (at a low or middle speed). The variable intake valve is opened by the actuator (in a state 33), sucked air moves a relatively short distance 30 and, thus, air in the surge tank 10 is supplied to the combustion chamber (not shown) through the outlet 70, if the speed of the vehicle exceeds the designated speed (at a high speed).
However, in this case, since one suction passage and one outlet are used both at a low or middle speed and at a high speed, the cross-section of the suction passage is not changed and thus it is difficult to provide air at a proper amount at a proper speed required according to speeds of the vehicle.
The above description has been provided to aid in understanding of the background of the present disclosure and should not be interpreted as conventional technology known to those skilled in the art.